There is an oscillation power generator (or reciprocating power generator) that converts kinetic energy of a reciprocating permanent magnet into electric energy (for example, see Patent Literature 1). In the description, the oscillation power generator (or reciprocating power generator) is referred to as a linear power generator. The linear power generator includes a reciprocating (oscillating) center yoke corresponding to a rotor of a rotary power generator and an outer yoke corresponding to a stator of the rotary power generator. Generally, a winding portion (coil portion) is provided on an outer yoke side, a permanent magnet is provided on a center yoke side, and power generated in the winding portion by reciprocating motion of the center yoke in the fixed outer yoke is taken out. In the rotary power generator, a technology of constraining cogging is frequently used in order to obtain a smooth motion of a rotating shaft (for example, see Patent Literature 2).